From DE 103 18 958 B3, it is known in the case of a drive means for an injection molding unit in an injection molding machine to attach the axial movement motor directly to the feed screw and to place the dispensing motor that is used for rotating the feed screw behind the axial movement motor as viewed from the plasticizing unit. The connection between a spindle passing thorough the axial movement motor and the rotor of the dispensing motor is effected in mutually non-rotatable manner but it is axially moveable with the aid of multi-tooth couplings (see also WO 2007134961 A1, U.S. Pat. No. 7,270,532 B2, DE 43 44 335 A1). The position of the axial movement motor relative to the dispensing motor does not change when the injection molding unit is in operation.
Furthermore, US 20060093694 A1, which has a comparable construction to DE 103 18 958 B3, comprises a blocking means 29 in the manner of a clutch which permits only unidirectional operation of the axial movement motor upon the occurrence of a certain force.
From EP 1 886 793 A1 or DE 10 2009 030 099 A1, a device is known in which a plasticizing unit that is known in the field of injection molding is coupled to a material storage device that is subjectable to pressure and is used for the production of a fluid phase of a material. The material storage device is a component of a discharge unit for delivering mutually succeeding drops for the purposes of constructing a three-dimensional object on an object carrier without the use of molds. Due to the adhesive forces of the material, a high pressure and usually also high temperatures are necessary for this purpose. At the same time, the thus produced parts, for production quantities in single and small batches such as samples for example, have to be precisely manufactured from very viscous fluid materials such as molten synthetic material in the smallest of quantities in discrete individual portions of down to just a few micrograms, so that the material has to be conveyed at very low speeds.
For producing the drops, 50 to 100 MPa (500 to 1000 bar) are present at the outlet opening of the discharge unit. Amongst other things, this is because of the so-called laminar source-flow which the material exhibits in the fluid phase. Contributing to the source-flow amongst other things is the accumulation of the melt on the wall. This can be seen most clearly by considering the knowledge gained from the field of injection molding. During the mold-filling process of a simple rectangular channel, the melt is injected via a so-called sprue point and begins to spread out from this point in a circular manner having closed flow fronts until it fills the entire width of the cavity. Some time thereafter, the region between the intake and the flow front can be regarded as almost formed. At the flow front itself however, a special flow situation prevails, the “source-flow”, since the flow lines in this region appear to be like a source, if one regards them with respect to a concurrently moving coordinate system.
The laminar source-flow is of advantage for the production of drops ‘aligned’ on the object that is to be manufactured due to its laminar formation on the one hand, but on the other hand, it is precisely here where the problems aggravating the adaptation of the devices and materials known from the field of injection molding arise, above all, in the formation of small drops. The wall adhesion leads to the fact that the masses can only be formed into drops having the desired small volumes, preferably in a range of less than or equal to 1 mm3 with great difficulty, whereas it is a correspondingly high viscosity of the material that is of prime importance for the formation of a suitable drop-shape of a drop.
This also differentiates the materials being used from the previously known waxes. Due to their viscosity, waxes can be expelled in normal thermoprinting or inkjet processes, i.e. by a purely kinematic, pressure-free acceleration process without a pressure difference of the melted drop. The materials used here differ from them because their coefficient of viscosity is higher by several orders of magnitude. Thus, the dynamic coefficient of viscosity of the solidifiable material lies between 100 and 10000 [Pa s], where the solidifiable material is preferably a synthetic material that is common in the field of injection molding or a resin. This makes it necessary for the fabrication process to make use of a pressurizable material storage device and hence too, a special pressure generating unit, since pressures of more than 50 to 100 MPa (500 to 1000 bar) are definitely required, especially when small discharge openings are used for producing drops having a small volume.
Preferably, the desired volume of the drop lies especially in a range of 0.01 to 1 mm3. The diameter of the outlet opening preferably amounts to about 0.1 mm. In the case of a quite normal injection speed of 100 [cms] which advances the mass through a so-called point gating of 0.1 [mm] diameter, there then results a value of 10,000 [ms] for the through surface flow rate. For the fluid phase, this leads to a laminar flow-source with flow velocities of up to 10,000 ms.
Comparable processes, which are commonly known by the expression prototyping and rapid manufacturing and are intended for the production of sample parts with the requirement for a very brief preparatory time, do not have this problem. The production of such parts is based on a mold-less process, i.e. without forming molds, namely, in most cases too, in the production of the geometry from 3D data, although these geometries are produced by appropriate means such as melting powder layers by the application of heat, e.g. by means of a laser, generative systems such as printing processes in differently linked forms of the powder particles or else by means of a so-called fusion stranding process. The precision of these processes is not affected at all by the pressure in the system or only to a small extent in the fusion stranding process, but a discontinuous production of the three-dimensional object does not take place there.